Process for dispersing pigments



Aug. 27, 1940. 2 R, T, H K 2,212,641

PROCESS FOR DISPERSING PIGMENTS Filed Dec. 27, 1951 2 Sheets-Sheet 1 Kobe]? (9/52" Hue/m JNVENTOR MG ATT RNL'Y Aug. 27, 1940. HucKs 2,212,641

PROCESS FOR DISPERSING PIGMENTS Filed Dec. 27, 1957 2 Sheets-Sheet 2 IIE R0567! @167 if 016/0" INVENTOR PatentcdAug. 27, 1940.

UNITED STATES PATENT "OFFlCE PROCESS FOR DISPERSING PIGMENTS.

Robert Tyler Hucks, South River, N. J., assignor to E. L du Pont de Nemours 8; Company, Wilmington, Del., a corporation of Delaware Application December 27, 1937, Serial No.181,951 r r 3 Claims.

This invention relates to the dispersion of pigments and more particularly to an improved process for dispersing pigments in coating com-j, positions.

According to known. processes of manufacturing pigmented lacquers or enamels, the pigment is broken up and dispersed in-the vehicle by intensive mechanical disintegration. This is usually carried out, for example, by grinding in variited because of the thin layers ofvehicle and pigment dealt with, whereas the cycle of operation of the conventional ball mill is extremely long.

One-half to inch diameter steel balls are normally used in the conventional type ball mill. It is possible to use a smaller diameter ball such as a /8 inch size, but to do so it is necessary to use a much thinner grinding vehicle in order to obtain the proper cascade efiect. The result of this is that the amount of pigment per charge is greatly reduced. A decreased grinding cycle is obtained which does not compensate for the smaller charge of pigment per mill. This invention has as an object the provision of a process for the dispersion of pigments which aifords substantial improvements, particularly as regards manufacturing economies, in that a short cycle of operation and savings in capital invest- ,ment are realized. Other objects-will appear hereinafter.

plan view of'the apparatus herein described. In the figure, the tank is indicated at I. The tank provided with a propeller! whichis driven by shaft '3 and motor The motor is supported.

by thecover '5. The tank is shown as containing the vehicle 6 and balls "I, the function of which will be more fully described hereinafter.

Figure 2 is a similar diagrammatic plane view of the apparatus herein described which is modilied to permit rotation of the tank 1. In both figures the same numerals refer to the same parts. In Figure 2' the motor 4 is supported on a frame it. The tank .-I is provided with an annular track Ii which bears against the rollers 8 and t9 in order to hold the tank in a vertical position.

.In the drawing, l igureil is-aZ-diagraminatic Any suitable number of these rollers may be provided. Two are shown although at least three are probably necessary. These rollers are mounted on a bracket l2. The rotation is provided by means of a spur and ring gear 13 and I4, respectively. The tank is mounted at its base on a ball or other bearing shown as l 5 which is mounted in a recess in the gear i4 and the base Hi to permit rotation. The spur gear I3 is driven by axle I1 mounted in a.bearing l8. The gear and axle l3 and I! are rotated by means of a separate motor or pulleynot shown.

These improvements are accomplished by the following invention which comprises dispersing a pigment by reducing the pigment agglomerates to an extremely fine state of subdivision by rapid propulsion of small steel balls in a suitable container, whereby the agglomerates of pigment are under intensive bombardment and are broken down in ashort time, not only from impact of the balls with each other, but from impact-between the balls and the walls of the container.

In contrast to the rotating movement of an ordinary ball mill, the container or mill utilized in the present invention. may be stationary and the contents agitated by means of a rapidly moving stirring device. The interior wall of the mill may be bailled or corrugated to aid in increasing the efiiciency of the apparatus. In some instances also, it may be desirable to construct the apparatus so that thecontainer may be caused to rotate counter -to the general movement of the metal balls, but at the present time the stationary container seems tofhave the greatest commercial adaptability from the standpointof economic construction. i

,Steel balls, inch 1n-diameter, and mill base consisting or pigment and a suitable vehicle such as resin'solutiom'plasticizer, etc., may be charged in a stationary one gallon Monel metal container, 7 inches in diameter, and the mixture agitated by use of a Lightnin mixer.- This mixer, which may be operated at 1750'R. P. M., has a threeblade propeller, 2 inches in diameter. The inch steel balls are-preferred because it is easier to separate them from the mill base after the grinding cycle; One-sixteenth inch diameter or smaller balls produce very satisfactory results, providing adequate means of separating them from the mill base are available. As a satisfactory means of separating the mill base or finished product from the balls, it is possible to magnetize the mill which will in turn hold the balls in place and permit ready removal of the charge.

The following examples are illustrative compositions which were prepared according to the process .of the invention:

i Example 1 V First portion: Percent Iron blue pigment 7.0 Zinc oxide 0.8 Blown castor oil, 3.7 Dibutyl phthalate 5.6' Damarresinsolution' 9.2 Gaso 5.3 Ethyl ac Butyl, acetate 3.2

'Second portion:

Buty] alr-nhnl 6.3 Butyl acetate 5.2 Ethyl nonfn'fp' 202 Gaso 5.4

Third portion:

Ethyl alcohol (denatured) 7.3 Cellulose nitrate 17.0

The ingredients of the first portion were agitated with A; inch steel balls for four hours according to the above procedure.

The ratio of steel balls to mill base charge (first portion) was 3-1. The materials of the second portion were added and mixed in thoroughly. The alcohol wet cellulose nitrate comprising the third portion was then added and mixed with this'com'position until the cellulose nitrate was dissolved to give a finished enamel.

An alternative procedure provides for the dispcrsion of the pigment in the first portion in the new type mill and the transfer of the same from the mill, preferably after the addition and further mixing of the second portion, to an ordinary paddle mixer. The ingredients of the third portion may then be added and the mixture thoroughly agitated until a homogeneous product is obtained. This method may also be employed as an alternative method for preparing other examples that follow.

Example 2 First portion: Percent Leaded zinc oxide; 11.2 Castor oil 3.6 Dibutylphthalate 5.7 Damar resin solution 9.7 Gasoline I 53 Ethyl acetate 3.3 Butyl acetate v 3.2 Second portion:

Butyl acetate 4.8 Gasoline 3.8 Butyl alonl'ml 5,8 Ethyl acetate 19.2 Third portion:

Ethyl alcohol (denatured) 7.3 Cellulose nitrate 17.1

The ingredients of the first portion were ground with inch diameter steel balls for one hour according to the procedure used in Example 1. The materials of the second portion were tained.

Example 3 First portion: Percent Toluidine toner 6.7 Castoro I 3.2 Dibutyl phthalate 5.0 Damar resin solution 8.5" Gasoline 10,0 Ethyl acetate 6.2 Butyl alcohol 2.7 Butyl acetate 3.3

Second portion:

Ethyl ace 17.4 Butyl alonhnl 5.6 Butyl acetate 4.4 Gasoline 3.? Toluol 1.9

Third portion:

Ethyl alcohol (denatured) 6.4 Cellulose nitrate 15.0

then added and mixed until the cellulose nitrate was dissolved and a homogeneous enamel secured.

In carrying out the mixing cycles after the addition of the second and third portions in this and previous examples, the speed of the agitator mixer may be considerably reduced since the work expended in grinding the first portion has satisfactorily reduced the pigment agglomerates and all that is needed subsequently is sufiicient agitation to thoroughly dissolve the cellulose nitrate and bring about uniformity and homogenity in the final enamel.

The viscosity characteristic of the cellulose nitrate used in the above examples, is about 3 seconds as determined in accordance with procedure outlined in A. S. T. M. specifications D-301-303, Formula B. While a cellulose nitrate of about this viscosity'characteristic is preferred, cellulose nitrates of somewhat higher or even lower viscosities may be utilized in preparing the enamel compositions of the present invention. It is preferably added to the composition wet with denatured ethyl alcohol as commercial alcohol wet cellulose nitrate as the third portion in the examples.

Metal balls fabricated from metals or metal alloys other than steel are likewise suited for to mill base charge in the examples is preferably 3 to l but other ratios are likewise operable and this factor may be varied under difierent operating conditions. 1

In order to establish a direct comparison, the first portion of Example 1 was prepared in a one gallon conventional rotating ball mill, using inch steel balls. The ratio of balls to mill base was 3-1. To equal the luster and color development of the enamel prepared according to the process of this invention, it was necessary to continue the ball mill grinding for 50 hours. Therefore, a comparison of four hours for small ball propulsion is presented against 50 hours for conventional ball mill grinding.

The process is also operable for the manufacture of other pigmented cellulose derivative enamels such as are prepared from cellulose acetate, ethyl cellulose, benzyl cellulose, etc. In these instances it will, of course, be necessary to employ resins, plasticizers and solvents which are compatible with the particular cellulose derivative used as the primary vehicle. Oleoresinous and synthetic resin enamels such as those prepared irom alkyd and other types of synthetic resins may be manufactured according to the process of the invention by suitable adjustment and variation in the liquid vehicle, such variations being well understood by those skilled in the art. In any event, however, the viscosity of the. vehicle formed by combining the several types of ingredients which go to make up the vehicle should be such that the velocity of the balls is not greatly retarded and certainly not so high as to appreciably reduce the impact forces of the balls. The types and proportions of the several mill base ingredients should be chosen and adjusted as to permit free movement of the balls under the selected operating agitation conditions to give proper propelling velocities.

In the examples, the steel balls are rapidly propelled by means of a rotating mixer operating at high speed. Other means may be employed for creating similar conditions. For example, the necessary rapid movement of the balls may be obtained by forcing blast of air or other gas through the mill base at such a rate as to cause the balls to be propelled at a. high velocity through the mixture, or the mill base containing the pigment, steel balls and liquid organic vehicle may be pumped through a container such as a pipe or connected series of pipes with or without baflles at such a rate as to set up a high turbulence causing rapid propulsion of the steel balls throughout the body of the mill base. Regardless of the source of energy employed to propel the steel balls, it should be such as to cause rapid propulsion of the steel balls which when they collide or strike the walls of the container cause high impact forces against the pigment agglomerates which are suspended between two striking surfaces, thereby breaking up and reducing the agglomerates to aflord a high degree of dispersion.

The process of this invention is not limited in its scope to any particular pigment or class of pigments, since it may be utilized in the dispersion of practically any of the pigments ordinarily used in the lacquer and enamel industry. The enamels prepared in accordance with the new process are characterized by unusually high gloss, depth of color and absence of pigment grit. Pigment dispersion, mixing and complete formulation of the enamel may be effected in this improved type of ball mill, and the finished composition drawn off at the base of the mill, thereby providing a definite saving in time and labor. A saving in capital investment of mill equipment is obvious in conjunction with the short operating cycle of this unique process of pigment dispersion.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof; and, therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. The process of dispersing pigments in a liquid organic vehicle which comprises placing the same in a closed container adding thereto a mass of steel balls having a diameter of approximately the ratio by weight of the steel balls to the combined other ingredients being about 3:1, subjecting the charge to a violent bombardment oi. the balls by rotating a, propeller at a speed of about 1750 revolutions per minute completely below the surface of the charge.

2. The process of dispersing pigments in a liquid organic vehicle which comprises charging the pigment and vehicle into a closed rotatable container, adding thereto a mass of small metallic balls. the weight of the balls being about three times the weight of the combined vehicle and pigment, and subjecting the mass to the action of a propeller rotating beneath the surface of the charge at a speed of about 1750 revolutions per minute.

3. In the process of dispersing pigments in a vehicle having a viscosity substantially that of ordinary lacquer or varnish wherein the charge is placed in a cylindrical container the axis of which is vertical, the improvement which comprises subjecting the vehicle and pigment to a violent bombardment action of steel balls the weight of which is about three times the weight of the vehicle and pigment, the said bombardment bein effected by a propeller rotating in substantially a horizontal plane at a speed of about 1750 revolutions per minute completely below the surface of the vehicle.

ROBERT TYLER BUCKS. ll 

